I made an observation of Gassendi on April 6, 2009 (05:30 U.T.) using my 9-inch (23-cm) F/13.5 Maksutov-Cassegrain at 359x under steady (6-7/10) seeing conditions and transparent skies (4-5/6). Gassendi (17.5*S, 39.9*W) is a prominent walled-plain located over the northern edge of Mare Humorum measures approximately 68 miles (110 km) in diameter with a central group of peaks as high as 0.75 miles (1.2 km) high. A complex set of rilles are noted over the floor of Gassendi named Rimae Gassendi. The crater located over the northern edge of Gassendi is Gassendi A (~21 miles (33 km) diameter) with Gassendi B (~16 miles (26 km) diameter) to the north of A. Gassendi is estimated to be 3.6 billion (thousand million, +/- 700 million years) years of age. The rim of Gassendi rises as high as 1.5 miles (2.5 km) above the floor of the plain, especially the northwest rim. The central peaks of Gassendi were considered a potential landing site for the Apollo 17 mission to the Moon, but the Taurus-Littrow Valley was chosen instead.

A digital image produced using Photoshop CS3.

Attached Files

I am providing a basic description of Photoshop (CS3) for a tutorial on the production of my Gassendi observation above. There exists many excellent articles, books, and web sites on using Photoshop as exemplified by the links below. Although I am describing Photoshop there exists many other excellent image editing software available such as Corel Paint Shop Pro (Corel Photo-Paint which is included in the excellent Graphics Suite is also an excellent program as exemplified by Rony De Laet), Gimp (a free and outstanding software) and many other programs not mentioned. Below is an image of the Photoshop CS3 workspace with the main feature of the program described.

Carlos

Attached Files

The Tools palette contains a diverse group of tools for image editing. If the tool contains a triangle at itâ€™s lower right corner than more tools are available by clicking on it. The tools that I employ the most are the brush tool, clone stamp tool, lasso tool, blur tool, magic wand tool, and the eyedropper tool.

Carlos

Attached Files

Upon opening (clicking upon) the brush tool a brushes palette is visible above over the options bar. If you click on the Brush option you will note a variety of brushes available. The first set of brushes (1-19) produce a hard edge. The second set (5-300) contain a dark core with a soft edge (I use these the most for renderings). The following sets vary the softness/hardness of the brush as well as other types of brushes. You can also create a new brush from the brushes palette from existing brushes or download new brushes and add them to the palette.

Attached Files

I use the Wacom Graphire 3 graphics tablet for my digital renderings. The active area (area which you may draw upon) of my tablet measures 4 x 5 inches. The tablet comes with a grip pen and mouse which are used over the active area. The grip pen provides 512 levels of pressure (the more expensive Intous tablet provides 2,048 levels of pressure). With practice the digital artist comes to depend upon the tablet as if using a pencil for their renderings.

Carlos

Attached Files

An outline of Gassendi (or any other object) is first produced using the pencil tool or a small brush from the brushes palette. You may want to keep the opacity of the pencil/brush to less than 30% as a darker line will be harder to erase. The majority of renderings amy be produced using a 600 x 600 pixel drawing area. The majority of observers make the mistake of making their observations too small and therefore overcrowd the drawing.

Carlos

Attached Files

The next step is the addition of shadows noted over the feature observed as noted by the red arrows. The application of a shadow may be done gradually (e.g. using a low opacity (20%) with repeated applications over an area).

Carlos

Attached Files

The next step is the addition of light and medium shadings. Be careful not to hide the faint pencil/brush marks initially applied. The the light blue arrows indicate the light shadings whereas the violet (purple) arrows indicate the dark shadings.

Carlos

Carlos

Attached Files

The mottled area over the southwest section of Gassendi is now developed as noted by the yellow arrows. Hummocky (low hills/ridges) terrain of Gassendi is developed over the northern half as well as north of it as indicated by the green arrows.

Attached Files

You have made a beautiful rendering of Gassendi with great practiced use of your digital equipment. I think it is worth a gallery presentation and award.

The tutorial is also quite useful and thoughtfully done. I wish I could just find a set-up here in Portland with so many amateur astronomers and artists and computer career types as I would like to try my hand at this. I know of no astronomers locally that have the Wacom CS3 system and grip pen mouse. I only use a simple Photoshop CS2 with standard mouse to crop, adjust contrasts, little touch-up and enhance photographs, (but never really change my original art images with it) before loading to the web.

I always look forward to your future sketches and great useful information. I recommended to a class of students that I lectured to yesterday at a college planetarium with all of my pastel sketch art, to see the cloudy nights sketching forums.

This tutorial is such a wonderful addition to the Sketching Forum. I'm going to ask Eric or Charlie to add it to the "Collection of Sketching Forum's 'How To' Threads". It's just this kind of contribution that makes this forum such a interesting and exciting resource for astronomical sketchers. Thank you for sharing your techniques with us all my friend!

The sketch is gorgeous in it's details and description, a hallmark of your astute approach to lunar drawing. I'm in awe of the way you handled the lighting and shadows. The rilles are very impressive, beautifully and delicately rendered. Bravo Carlos!

Thanks so much for the digital sketching tutorial. I've been waiting for this ever since you mentioned that you were planning to present it. Appreciated even more so given what must be a hectic professional schedule. I can't wait to try and apply some of these techniques.

Thank you all very much for the heartfelt compliments on my Gassendi observation and digital tutorial. My reward is being able to help my fellow observers better understand the tools available to them in making astronomical sketches of the heavens. The observations provided by you all on this forum have inspired me to make my own observations. I am sorry that I have not provided more tutorials on a regular basis but my work schedule has prevented me from doing so. I truly appreciate the recognition from my fellow observers who are very talented themselves.

I am honored that this observation/tutorial has been placed in the "How To" section of the forum. I hope that it helps future observers in their own observations.

Didn't see this until today but what a wonderful sketch and more importantly thanks for the digital tutorial. I've gathered some insights that I think will crossover and help me in GIMP. You make an excellent point about overcrowding the drawing. Thanks for sharing the information!

Thank you for the compliment on my Gassendi observation. It is my pleasure to be able to provide the tutorial for all to learn from. I hope to be able to provide a tutorial using Gimp in the future as well.

Thank you for the compliment on my Gassendi observation/tutorial. I enjoyed it as I hope that it will help others use electronic media in the future. Please continue to make your excellent classic observations in the future.

This is most impressive. I can see doing this for a deep sky object with much time and practice. It would take me more than a year to begin to do this on a lunar landscape. I have a new appreciation for your dedication to electronic sketching.